1. Field of the Invention
The subject invention is directed to a fuel injector for a gas turbine engine, and more particularly, to a radially outwardly flowing air-blast fuel injector for a gas turbine engine.
2. Description of Related Art
Air-blast fuel injectors for issuing atomized fuel into the combustor of a gas turbine engines are known in the art. Also known in the art are staged fuel injectors designed to improve engine efficiency. Here, the combustion process is divided into two or more stages or zones, which are generally separated from each other, either radially or axially, but still permitted some measure of interaction. For example, the combustion process may be divided into a pilot combustion stage and a main combustion stage. Each stage is designed to provide a certain range of operability, while maintaining control over the levels of pollutant formation. For low power operation, only the pilot stage is active. For higher power conditions, both the pilot and main stages may be active. In this way, proper fuel-to-air ratios can be controlled for efficient combustion, reduced emissions, and good stability.
One example of a staged fuel injector is disclosed in U.S. Patent Application Publication No. 2006/0248898 to Buelow et al. The injector includes a radially outer main pre-filming fuel delivery system, and an on-axis pilot pre-filming fuel delivery system. Another example of a staged air-blast fuel injector is disclosed in U.S. Pat. No. 6,272,840 Crocker et al. Here the main fuel delivery system is a pre-filming air-blast type atomizer and the pilot fuel delivery system is either a simplex air-blast type atomizer or a pre-filming air-blast type atomizer.
In prior art staged pre-filming air-blast type atomizers such as those described above, fuel in the main and pilot delivery systems exits from a fuel circuit, and flows radially inward to form a fuel sheet on a filming surface. High-speed air is directed over the filming surface to effect atomization of the fuel and mixing of the fuel and air. High-speed air is also directed across the exit lip of the filming surface to enhance atomization and control the resulting spray cone angle of the atomized fuel.
In addition to staged combustion, providing a thoroughly blended fuel-air mixture prior to combustion can significantly reduce engine emissions. While the prior art staged pre-filming air-blast type atomizers described above can provide a well blended fuel-air mixture, it is desirable to provide an air-blast atomizer designed to even more thoroughly mix fuel and air prior to combustion. This would lead to still further reductions of engine emissions and pollutants.